1. Field of the Invention
The present invention relates to a shielding apparatus for an electronic device, and more particularly to a shielding apparatus for an electronic device capable of reducing or eliminating electromagnetic interference.
2. Description of Related Art
A quartz oscillating device is composed of a quartz crystal, an oscillator and a clock generator. In the aspect of application, the quartz oscillating device can be soldered on the surface of the circuit board by the surface mount technology (SMT) or the plated through hole (PTH) technology for providing desired clock signals under a specific operational frequency to micro-processors or the other high-level or low-level micro-processing chips. Therefore, the quartz oscillating device can be widely applied to personal computers, portable computers, liquid crystal displays, high-level communication products, broadband network, such as ADSL, network hubs, 10/100 MHz switchers, routers and the other high-frequency products.
In the present population of electronic apparatus, a variety of quartz oscillators and voltage-controlled oscillators (VCO) are applied to the internal circuits of the electronic apparatus. All these electronic devices can be the sources of electromagnetic radiation. Therefore, it is desired to prevent electromagnetic interference for fitting the electromagnetic interference standard. The research and development of the quartz oscillating device with low electromagnetic interference (EMI) are essential in this industry to reduce noise/signal ratio and maintain high transmission quality.
FIGS. 1 and 2 are schematic drawings showing two prior art electronic devices for preventing EMI. Referring to FIG. 1, the electronic device 100, such as a quartz oscillating device or an oscillating devices vulnerable to EMI, is disposed on the surface of the circuit board 110 by the lead-inserting technology, such as DIP leads. The electronic device 100 is electrically connected to the circuit board 110 through the leads (not shown) by soldering for providing clock signals with accurate periodic oscillation as referential frequency or timing for micro-processors (not show). Additionally, the electronic device 100 has a metallic shell 102, such as a stainless-steel shell or an aluminum-alloy shell, for preventing electromagnetic radiation or the noises resulting form EMI. In order to preventing EMI, the prior art technology electrically connects the ground terminal of the electronic device 100, such as the metallic shell 102, and the ground terminal of the circuit board 110, such as the ground plate, by directly soldering 112 for reducing noises from EMI. Referring to FIG. 2, in the prior art technology, the ground terminal of the electronic device 100, such as the metallic shell 102, electrically connects with the ground terminal of the circuit board 10, such as the ground plate by welding the external lead 114 for reducing noises from EMI.
However, directly soldering 112 or welding the external lead 114 would generate high temperature, which could destroy the vibration stability of the quartz oscillating device as to generate substantial deviation. Additionally, the manual welding process need high costs, which does not meet economic requirement. The direct soldering method has the disadvantage that the adhesion of tin on the stainless-steel shell 102 is poor which would create the difficulty of manufacturing, low yield of the soldering contact 112 and looseness during oscillation tests. Therefore, the reliability of the assembly is substantially reduced.